This invention relates to electrochemical cells. Most particularly, it relates to electrochemical cells having an alkali metal anode, an electronically conducting cathode and a nonaqueous electrolytic solution having an inorganic oxyhalide solvent.
Modern technology has placed increased emphasis on producing an electrochemical power source having improved reliability, light weight, high power and long life. Power sources meeting these requirements find ready civilian and military applications in communications, entertainment products, portable light sources and weapon systems.
Various high-voltage, high-energy density electrochemical cells have been the subject of recent investigation. Much of the work in this area has been involved with electrochemical cells having negative electrodes comprising highly reactive metals such as lithium.
Work on electrolytes or electrolytic solutions for lithium-based electrochemical power sources has progressed generally along two major lines: High temperature molten salt electrolytes and organic solvent based electrolytic solutions. A cell which utilizes a molten salt electrolyte provides a chemically stable system in which strong oxidants such as chlorine can be reduced at conductive cathodes such as carbon. A cell utilizing a lithium anode and a carbon cathode upon which chlorine is reduced provides exceptionally high energy and power density making development of a practical cell with these materials of particular interest. The molten salt lithium/chlorine cell (having a lithium anode, carbon cathode and a molten salt, typically lithium chloride, electrolyte) has many characteristics desirable in a high performance electrochemical cell. The anode is highly electropositive, and the compound being reduced is highly electronegative. The equivalent weight of the reaction product is low and the anode, cathode and electrolyte conductivities are high. Nevertheless, these cells have severe problems. The temperature range of operation, which for the lithium chloride electrolyte is 450.degree.C to 650.degree.C, necessitates heating systems and insulation that increase its cost, weight and complexity; auxiliary systems are needed to collect and store the chlorine evolved in rechargeable cells at these high temperatures; and there are few materials that can withstand for extended periods the attack of molten lithium, chlorine, and molten lithium chloride at these temperatures.
In parallel with the development of lithium cells with molten salt electrolytes, lithium cells with non-hydroxylic organic solvent-based electrolytic solutions have been developed. These cells have been called "organic electrolyte cells" although typically they employ electrolytic solutions consisting of inorganic solvents. Cells of this type have the advantage of being operable at room temperature; however, chlorine itself and other strong oxidants cannot be used as a cathode with these solvents since the solvents are oxidized. Therefore, cells of this type will not provide an energy density as high as a lithium/chlorine cell.
In application Ser. No. 342,233 filed Mar. 16, 1973, and assigned to the assignee of the present invention, and now abandoned, there is described an electrochemical cell having an anode selected from a specific group of materials, including lithium, a cathode selected from a wide range of materials, and an electrolyte including an inorganic solvent, specifically phosphorus oxychloride, and a solute, selected from a wide range of materials, dissolved in the solvent.
In application Ser. No. 305,811 filed Nov. 13, 1972, and assigned to the assignee of this application, there is described electrochemical cells wherein the phosphorus oxychloride solvent is admixed with a low freezing solvent material to extend the operating range of the phosphorus oxychloride cell to temperatures below about 0.degree.C.
In application Ser. No. 419,568 filed Nov. 28, 1973, and assigned to the assignee of this application, there are described further electrochemical cells having thionyl chloride, sulfuryl chloride, and mixtures thereof as the solvent material.
In application Ser. No. 492,316 filed July 26, 1974, and application Ser. No. 517,557, filed Oct. 24, 1974, both assigned to the assignee of this application, there is disclosed, respectively, the use of carbon and (C.sub.4 F).sub.n active cathode materials as surfaces upon which the solvent material is catalytically reduced, thereby yielding cells utilizing the otherwise "dead" weight of the solvent material as an energy source.
In application Ser. No. 325,467, filed on Jan. 22, 1973, now U.S. Pat. No. 3,922,174, and assigned to the assignee of this application, cells having the same anode, cathode and electrolytic solution as set forth in the aforementioned applications and housed in a titanum or titanium alloy container are described.